Re: Contactor question, Arc Suppressioni

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Adam,

Arc suppression is best performed with a series resistor and 
capacitor across the contacts or across the load. There are no 
default values to use for arc suppression due to the various contact 
material, shape, size, and of course, various loads. Trial and error 
is best. In other words, literally viewing the contacts in a darkened 
room and changing the RC values until arc suppression is obtained. 
Usually, this means decreasing the R value (and it will be quite low).

For example, about 4 years ago, we had a board at work which a 
previous engineer designed. We were getting 20 boards a week failing, 
all due to excessive material transfer of the contact points which 
quickly welded closed, and due to this particular relay design, 
shorted power to ground frying the board. Besides changing the 
circuit to prevent a short should the contact weld closed, I also 
used a resistor and capacitor across the contacts "at the relay" 
which was the last to turn off (via new time delay just so I could 
direct the arc potential to a particular set of contacts). Through 
trial and error, I eventually stopped the relay arcing (I think I 
ended up at 0.1 ohms and 100uF) for this particular relay. We haven't 
had a relay fail in the past 4 years since this effort, so arc 
suppression really does work when it's done right. Of course, if some 
engineer down the road changes the relay (or if the manf. makes a 
change), then we may begin to see failures and go through the routine 
again. Of course, if it was mechanically designed "smarter", none of 
this would have been necessary. ;-)

Take care,
Bart

Tesla list wrote:

> Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>
>
> <snip> Also I've heard of folks placing
> capacitors across the contacts, to minimize arcing.
>
> Adam